LXR is a transcription factor. The orphan nuclear receptors, LXRα and LXRβ (collectively LXR) play a role in the maintenance of cholesterol balance. Peet et al., Curr. Opin. Genet. Dev. 8:571-575 (1998). In addition, LXR binds to the ATP Binding Cassette Transporter-1 (ABCA1) gene and increases expression of the gene to result in increased ABCA1 protein. ABCA1 is a membrane bound transport protein that is involved in the regulation of cholesterol efflux from extrahepatic cells onto nascent HDL particles. Mutations in the ABCA1 gene are responsible for genetic diseases that result in the complete absence or low levels of HDL cholesterol and a concomitant highly increased risk of cardiovascular disease. See Brooks-Wilson et al., Nat. Genet. 22:336-345 (1999); Bodzioch et al., Nat. Genet. 22: 347-351 (1999); and Rust et al., Nat. Genet. 22:352-355 (1999). ABCA1 knockout mice homozygous for the mutation in the ABCA1 gene have virtually no plasma HDL, whereas the heterozygotes produce 50% of the HDL of wild type animals. See, Orso et al., Nat. Genet. 24:192-196 (2000) and McNeish et al., Proc. Natl. Acad. Sci. USA 97:4245-4250 (2000). ABCA1 knockout mice also show increased cholesterol absorption. See, McNeish et al., Proc. Natl. Acad. Sci. USA 97:4245-4250 (2000). Increased expression of ABCA1 results in increased HDL cholesterol, decreased absorption of cholesterol, and increased removal of excess cholesterol from extrahepatic tissues, including macrophages. LXR agonists also upregulate macrophage expression of apolipoprotein E and ABCG1, both of which contribute to the efflux of cellular cholesterol. By stimulating macrophage cholesterol efflux through upregulation of ABCA1, ABCG1, and apoE expression, as well as increasing the expression of other target genes including cholesteryl ester transfer protein and lipoprotein lipase, LXR agonists influence plasma lipoproteins.
Accordingly, compounds which function as LXR modulating agents, and particularly as LXR agonists, would be useful in methods of increasing ABCA1, ABCG1, and apolipoprotein E expression, increasing cholesterol efflux from peripheral cells, and treating LXR mediated diseases and conditions such as cardiovascular disease and inflammation.